1. Field of the Invention
The present invention relates to a paper feeding/conveying apparatus which is arranged on the lower side of an image forming apparatus, has paper feeding containers arranged at plural stages within a housing, raises sheets of paper fed from these paper feeding containers by a vertical conveying means and feeds the sheets of paper to the image forming apparatus. The present invention also relates to a method for feeding and conveying a sheet of paper.
2. Description of the Related Art
An image forming apparatus is constructed by a copying machine, a laser printer, a facsimile, etc. A space for an office automation (OA) equipment such as the image forming apparatus has been recently reduced. In a paper feeding/conveying apparatus, a plurality of paper feeding cassettes or paper feeding trays are stacked with each other in a vertical direction. Such a paper feeding/conveying apparatus is formed and separated from a body of the image forming apparatus. The paper feeding/conveying apparatus is arranged on a lower side of the body of the image forming apparatus to reduce an area for arranging the paper feeding/conveying apparatus. The paper feeding/conveying apparatus having such a structure has gradually spread.
In general, a proposed and used paper feeding/conveying apparatus of this kind is disclosed in e.g., Japanese Utility Model Application Laying Open (KOKAI) No. 1-78629.
A method for conveying a sheet of paper by frictional force of each of elastic rollers is used in such an apparatus and uses a simple structure so that this method is widely used. However, in such a method, a coefficient of friction of rubber used for the elastic conveying rollers is reduced with the passage of time. Further, a slip of the conveying rollers is caused by the generation of paper powder and the sheet of paper is jammed in a connection section between the conveying rollers and guide plates since the sheet of transfer paper is wound therearound in an environment of high humidity.
In Japanese Utility Model Application No. 1-78713, the same applicant as this patent application proposed a paper feeder for a printer having a simple structure. In this structure, a sheet of paper is fed by a single paper feeding roller to a recording section from plural paper feeding trays stacked with each other in a vertical direction.
In a conveying mechanism having this structure, a slidable paper feeding base is further arranged on paper feeding bases of a general one tray system in a paper conveying direction. Accordingly, in consideration of a layout of this mechanism, it is difficult to store a large amount of sheets such as 1000 sheets of paper on one paper feeding base. To store such a large amount of paper sheets on one paper feeding base, the size of a paper feeding section is increased so that the entire printer is large-sized.
Further, such a paper feeding base including plural paper feeding trays having sheets of paper thereon must be moved in the vertical direction every time a size and a kind of the sheets of paper are changed and the position of an upper face of the sheets of paper within a cassette is lowered from an allowable range during a paper feeding operation. Accordingly, a large power is required to operate this mechanism.
In Japanese Patent Application No. 1-117374, the same applicant as this application proposed a very novel conveyer for conveying a sheet member, etc. In this conveyer, an alternating electric charge density pattern is formed on an endless belt made of a dielectric substance. Thus, the sheet member is adsorbed and conveyed by adsorbing force generated by this electric charge density pattern.
However, in this proposal of the conveyer, no method for feeding sheets of paper stored on a paper feeding tray, etc. is shown. In this proposal, the sheets of paper are fed by a general paper feeding roller, etc. as a premise. In this respect, no problems about the above general paper feeding/conveying apparatus can be completely solved.
For example, Japanese Patent Application Laying Open (KOKAI) No. 59-212856 discloses a paper conveyer for an electrophotographic copying machine. In this paper conveyer, no paper feeding trays are arranged at a plurality of stages. However, a single insulating endless belt is used to feed and convey a sheet of transfer paper from a paper feeding section of the copying machine to an inserting section of a fixing device through a transfer section. A method for adsorbing the sheet of transfer paper to the endless belt is different from an adsorbing method using the adsorbing principle applied by forming the above-mentioned electric charge density pattern. Namely, in this adsorbing method, the insulating endless belt is charged by using a charging means to electrostatically adsorb the sheet of transfer paper by a difference in potential between the sheet of transfer paper and the insulating endless belt.
In accordance with this conveying method, it is possible to reliably convey the sheet of paper without any fear of the generation of a paper jam, etc. Further, the structure of a conveying mechanism is simplified and cost thereof is simultaneously reduced. Further, no paper powder is generated, or an amount of the paper powder is greatly reduced since the conveying means and the sheet of paper do not come in frictional contact with each other.
Japanese Patent Application Laying Open (KOKAI) No. 63-139846 discloses another paper conveyer. In this paper conveyer, a paper feeding section of a copying machine, a resist section, a transfer section, a fixing section and a paper discharging section are sequentially connected to each other through a single endless belt. First, the endless belt comes in press contact with a sheet of copy paper held by a copy paper feeding/holding section. The sheet of copy paper is then discharged from the copy paper feeding/holding section by frictional force. After a resisting operation of this sheet, the paper sheet is conveyed to the transfer section and a toner image is transferred onto this paper sheet by a photosensitive body. Then, the paper sheet is fixed by the fixing section and is discharged therefrom.
In this paper conveyer, it is possible to simply and reliably move the sheet of copy paper and each of the respective constructional sections in the copying machine, and control the movement of the sheet of copy paper in a feeding direction thereof.
However, each of the above-mentioned various devices for feeding and conveying a sheet of paper by using the above endless belt is used to feed the sheet of paper from a single paper feeding tray. Accordingly, such devices cannot be used in a multistage paper feeding/conveying apparatus in which paper feeding containers are arranged at plural stages in a vertical direction.